Process for the preparation of (r,s)-nicotine

ABSTRACT

A process for (R,S)-nicotine is described. Condensation of 1-(but-1-enyl) pyrrolidin-2-one with nicotinic acid ester gave 1-(but-1-enyl)-3-nicotinoylpyrrolidin-2-one which on treatment with an acid and a base gave myosmine. Myosmine was converted to (R,S)-nicotine by reduction followed by N-methylation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from India Application Ser. No.407/CHE/2011, filed on Feb. 14, 2011, entitled A PROCESS FOR THEPREPARATION OF (R,S)-NICOTINE, which application is assigned to the sameassignee as this application and whose disclosure is incorporated byreference herein.

FIELD OF THE INVENTION

The present invention describes a synthetic process for the preparationof (R,S)-nicotine.

BACKGROUND OF THE INVENTION

Nicotine, (S)-3-(1-methyl-2-pyrrolidinyl) pyridine, is an alkaloid foundmainly in tobacco. Smoking of tobacco results in nicotine dependence andis habit forming. Smoking has also been associated with disease of lungsincluding malignant growth. There is a world-wide recognition of harmfuleffects of smoking. Unfortunately habitual smokers find it very hard toachieve abstinence from smoking. Further dependence on nicotine comes inthe way of any effort to control smoking. To overcome this formidableissue, products containing small amounts of nicotine have been developedand are being promoted as substitutes for traditional smoking productslike cigars and cigarettes. Treating nicotine dependence requirestherapeutic use of nicotine. Nicotine is given to patients throughdermal patches, gums, creams, lozenges, nasal sprays or electriccigarettes to wean them away from smoking. Nicotine is alsotherapeutically used in treating certain medical conditions such asattention deficit disorder, Tourette's syndrome, schizophrenia,Alzheimer's disease, Parkinsonism etc.

The main source of nicotine is tobacco. Nicotine isolated from tobaccocontains many related minor alkaloids as impurities in addition toimpurities formed through degradation. European Pharmacopoeia monographon nicotine prescribes limits for anatabine, anabasine, cotinine,myosmine, β-nicotyrine, nicotine-N-oxide and nornicotine impurities,with a maximum of 0.3% for each of these but total being limited to notmore than 0.8%. British Pharmacopoeia also mentions anatabine, cotinine,myosmine, β-nicotyrine, nicotine-N-oxide as impurities. Although the USPdoes not mention specific impurities, a limit of 1% for all theimpurities and not more than 0.5% for any one impurity is prescribed.The impurities present in natural nicotine vary depending on thegeographical source of tobacco and the season in which it is collected.It is difficult to remove these impurities since they are closelyrelated. Thus the pharmacopoeias recognize the variations in quality andquantity of impurities in natural nicotine.

It was envisaged that nicotine obtained from synthetic source will befree from the impurities present in natural nicotine. Further, syntheticnicotine produced by a validated process with well characterizedimpurity profile should be a superior API compared to natural nicotinewith its varying impurity profile.

Several synthesis of (S)-nicotine are reported in the literature. Chiralcenter has been created by using expensive chiral intermediates such asprolinol (J. Org. Chem. 1982, 41, 1069-1073),pivaloyl-β-D-galactosylamine (Tetrahedron Letters, 1999, 40, 7847-7650),or using chiral catalyst (Synlett 2009, 9, 1413-1416). However, thesemethods are expensive and are not suitable for industrial production.

SUMMARY OF THE INVENTION

Since the enantioselective synthesis is too expensive on an industrialscale, synthesis of (R,S)-nicotine followed by resolution andracemisation of unwanted (R)-nicotine was explored.

The resolution of (R,S)-nicotine is reported in the literature. Aceto etal have resolved the racemic nicotine using d-tartaric acid (J. Med.Chem. 1979, 22, 174-177). DeTraglia and Tometsko have resolved(R,S)-nicotine using Pseudomonas putida cultures (Applied andEnvironmental Microbiology, 1980, 39, 1067-1069). Racemization of(S)-nicotine is also reported in the literature (SyntheticCommunications, 1982, 12, 871-879)

We have developed a new and efficient process for the synthesis of(R,S)-nicotine. Together with the known methods for its resolution andracemization of the unwanted isomer, this process provides an attractiveand economical method for the production of synthetic (S)-nicotine. Itwill be an alternative to natural nicotine, which has severaldisadvantages as mentioned earlier.

DETAILED DESCRIPTION OF THE INVENTION

The process for the preparation of (R,S)-nicotine is outlined in Scheme3 below:

The most convenient way to prepare (R,S)-nicotine is through myosmine(Scheme-3). Myosmine is hydrogenated to (R,S)-nornicotine, which onN-methylation gives (R,S)-nicotine.

Myosmine has been prepared by condensing N-vinylpyrrolidone with ethylnicotinate. (Acta. Chem. Scand. B. 1976, 30, 93). However, preparationof N-vinylpyrrolidone involves use of acetylene gas at high temperatureand pressure. N-vinylpyrrolidone is lachrymatory and irritating to theskin, lungs, and eyes. It is known to cause corneal opacity. Our effortsto find a safer alternative resulted in the selection ofN-(1-Butenyl)-2-pyrrolidone (I, scheme-3) which has not been used tillnow to prepare myosmine. N-(1-butenyl)-2-pyrrolidone (I) is a stable,colorless liquid and is not lachrymatory. Its preparation, as reportedin the literature, involves reacting butanal with 2-pyrrolidone in asolvent using p-toluenesulfonic acid as a condensing agent (ChemistryLetters, 1992, 247-250). Sulfonic acid and its esters are considered tobe potential alkylating agents that exert genotoxic effects. Because ofthis, use of p-toluenesulfonic acid is avoided in industrial processes.Earlier literature describes several other catalysts such as sulfuricacid and neutral or acidic alumina for condensing the aldehyde with2-pyrrolidone (Chemistry Letters, 1992, 247-250). In our hand, none ofthese catalysts gave satisfactory results. Kwon et al. had condensed(S)-ethyl pyroglutamate with butanal using phosphorous pentoxide ascatalyst (J. Org. Chem. 1992, 57, 6169-6173) to obtain(S)-ethyl-N-(1-butenyl) pyroglutamate. When we tried phosphoruspentoxide, it was found to be an excellent condensing agent and gave Iin good yields. Phosphorus pentoxide is soluble in water and can beremoved by alkali wash during workup to give phosphate salt, which isnot injurious to health on dilution. Phosphate salts are routinely usedas fertilizers and in food industry. In the next stage, I was condensedwith methyl nicotinate using sodium hydride in a solvent such as THF orDMF to obtain 1-(but-1-enyl)-3-nicotinoylpyrrolidin-2-one (II) in goodyields. To our knowledge II is a new molecule and is not reported in theliterature till now. Reaction of II with strong mineral acid such ashydrochloric acid under heating resulted in the deprotection of amidenitrogen, followed by decarboxylation to give a primary amineintermediate which on treating with base resulted in cyclization to givemyosmine. This is the first report of the preparation of myosminestarting from II. Catalytic hydrogenation of myosmine resulted in(R,S)-nornicotine. Haines et al used palladium oxide in ethanol toreduce myosmine to (R,S)-nomicotine and isolated (R,S)-nornicotine onlyas picrate salt (J. Amer. Chem. Soc., 1945, 1258-1260). Jacob usedsodium borohydride in methanol-acetic acid to reduce a related compound,5-bromomyosmine to obtain racemic 5-bromo-nornicotine

(J. Org. Chem., 1982, 47, 4165-4167). Hatton et al. used palladium onactivated carbon in methanol to reduce myosmine labeled with stableisotope, [6-²H]-myosmine to [6-²H]-nornicotine (J. Label Compd.Radiopharm. 2009, 52, 117-122). After screening a number of catalysts,we selected palladium on carbon with methanol as medium. After generalworkup, the pure (R,S)-nornicotine was isolated by high vacuumdistillation in high yields and high purity. Conversion of(R,S)-nornicotine to (R,S)-nicotine was carried out by N-methylationusing formaldehyde and formic acid as reported in the literature (J.Amer. Chem. Soc., 1993, 115, 381-387).

The embodiments of the present invention are illustrated in thefollowing examples, which are not intended in any way to limit the scopeof the invention.

EXAMPLES Example-1 A. Preparation of 1-(but-1-enyl) pyrrolidin-2-one (I)

A solution of 2-pyrrolidone (50 g, 0.588 mol), butanal (42.4 g, 0.588mol) and P₂O₅ (2 g , 0.014 mol) in 300 ml toluene, were refluxedtogether for 10 hours using Dean-Stark apparatus to collect liberatedwater. The resulting solution was cooled and washed with 5% solution ofsodium bicarbonate and dried over anhydrous sodium sulphate. Afterremoving the solvent under reduced pressure, 1-(but-1-enyl)pyrrolidin-2-one (I) was obtained by distillation as a liquid.

(68.2 g, 83.2%). ¹H NMR (CDCl₃): δ 1.02 (3H,t), 2.03-2.15 (4H, m), 2.45(2H, t), 3.5 (2H, t), 5.01 (1H, m), and 6.85 (1H, d). ¹³C-NMR (CDCl₃): δ172.52, 122.91, 113.8, 45.09, 31.07, 23.03, 17.27, and 14.27. IR: 2962,2930, 1698, 1663, 1253 Cm⁻¹.

B. Preparation of 1-(but-1-enyl)-3-nicotinoyl-pyrrolidin-2-one (II)

Sodium hydride (8.63 g, 0.36 mol of 60% dispersion in a mineral oil) waswashed with toluene to remove mineral oil. To this 20 ml ofdimethylformamide (DMF), 1-(but-1-enyl) pyrrolidin-2-one (25 g, 0.1798mol) and a solution of methyl nicotinate (20.94 g, 0.152 mol) in 15 mlof DMF were added. The reaction mixture was heated at 90° C. for 2 hrs.DMF was partially removed under reduced pressure, 50 ml water added,further cooled to 0-10° C. and pH adjusted to 7 using HCl. The reactionmixture was extracted with ethyl acetate and dried over Na₂SO₄. Afterremoving the solvent under reduced pressure a yellow solid was obtained,which on recrystallisation with diisopropyl ether gave1-(but-1-enyl)-3-nicotinoyl-pyrrolidin-2-one (II, 35.1 g, 94% yield),95% HPLC, M.R: 65-66° C. ¹H NMR (CDCl₃): δ 9.3 (1H,d), 8.8 (1H,d),8.41(1H, dt), 7.4 (1H,m), 6.76 (1H,d), 5.0 (1H,m), 4.5 (1H,m), 3.57-3.67(2H, m), 2.7 (1H,m), 2.3 (1H, m), 2.0 (2H,m), and 1.0 (3H, t). ¹³C-NMR(CDCl₃): δ 194.4, 167.1, 153.7, 150.4, 137.0, 134.4, 131.2, 123.3,114.9, 51.7, 44.2, 23.2, 22.3, and 14.26. IR: 2966, 2937, 2855, 2847,1631, 1613, 1489 Cm⁻¹.

C. Preparation of Myosmine

A mixture of 1-(but-1-enyl)-3-nicotinoylpyrrolidin-2-one (II), (40 g,0.1639 mol), 50 ml water and 85 ml HCl were refluxed together for 12hrs. The reaction mixture was cooled to room temperature, washed with 50ml×2 ethyl acetate, further cooled to 0° C. and pH adjusted to >13 usingNaOH. The reaction mixture was extracted with 100 ml×3 ofdichloromethane and the extract dried over Na₂SO₄. After removing thesolvent under reduced pressure, the crude solid obtained was purified byhigh vacuum distillation to give colorless solid myosmine (16.75 g,70%). ¹H NMR (CDCl₃): δ 2.05 (2H, m), 2.94 (2H, t), 4.06 (2H,t), 7.34(1H, dd), 8.18 (1H,dt), 8.64 (1H, dd), and 8.99 (1H, d). ¹³C-NMR(CDCl₃):δ 170.56, 151.1, 149.1, 134.6, 130.0, 123.3, 61.5, 34.7, and 22.5. IR:2961, 1620, and 1590 Cm⁻¹.

D. Preparation of Nornicotine

Myosmine (32 g, 0.219 mol) was dissolved in 150 ml of methanol andhydrogenated at atmospheric pressure with 1.3 g of 10% palladium oncarbon as catalyst. After 5 hours the mixture was filtered and thefiltrate was concentrated to get a brown solid (32 g, 94.9% purity byGC). It was further purified by vacuum distillation at 0.1 mm Hg to getpure nornicotine (27.46 g, 84.7% yield, 97.5% purity by GC). ¹H NMR(CDCl₃): δ 1.66-2.72 (2H,m), 3.0 (2H,m), 4.13 (1H,t), 7.24 (1H,m), 7.69(1H, dt), 8.46 (1H,dd), and 8.59 (1H,d). ¹³C-NMR (CDCl₃): δ 148.4,148.1, 140.16, 134.1, 123.3, 60.0, 46.8, 34.2, and 25.4. IR: 3291, 2960,1641, 1578 Cm⁻¹.

E. Preparation of (R,S)-Nicotine

To a solution of nornicotine (50 g 0.338 mol) in 100 ml water a mixtureof 37% formaldehyde (49.7 g, 1.656 mol) and 85% formic acid (37.26 g0.81 moles) was added and stirred at 85° C. for 20 hrs. The reaction wascooled and pH adjusted to >13 using NaOH, extracted with dichloromethane(100 ml×3) dried over Na₂SO₄ and solvent removed completely to get crudeoil (52.5 g, 94.33% purity by GC). It was further purified by highvacuum distillation at 0.1 mm Hg to obtain colorless (R,S)-nicotine(44.54 g, 81.3% yield, 99.1% purity by GC). ¹H NMR (CDCl₃): δ 1.72-2.0(3H,m), 2.1 (3H,s), 2.25 (1H,m), 2.3 (1H,m), 3.08 (1H,m), 3.23 (1h,t),7.25 (1H,m), 7.69 (1H, dt), and 8.5 (2H,m). ¹³C-NMR (CDCl₃): 149.71,148.76, 139, 134.97, 123.7, 68.9, 57.1, 40.5, 35.5, and 22.83. IR: 3233,1642, and 1402 Cm⁻¹.

Example-2 Preparation of Myosmine from I

Sodium hydride (17.26 g, 072 mol of 60% dispersion in a mineral oil) waswashed with toluene (25 ml×2) to remove mineral oil and added to 25 mlof DMF. To this a solution containing 1-(but-1-enyl)-pyrrolidin-2-one(I, 50 g, 0.3597 mol) and methyl nicotinate (41.8 g, 0.3057 mol) in 50ml of DMF was added. The reaction mixture was heated to 90° C. for 2hrs. DMF was partially removed under reduced pressure and 100 ml waterand HCl (165 ml) were added. The reaction mixture was heated to 110° C.for 12 hr, cooled and washed with ethyl acetate (50 ml×2). The aqueouslayer was cooled to 0° C., pH adjusted to about 14 using NaOH, extractedwith dichloromethane (100 ml×4), the extract dried over Na₂SO₄, thesolvent removed completely and the crude solid was purified by highvacuum distillation to get myosmine (34.38 g, 77.2% yield, 98.5% purityby GC).

1. A process for the preparation of a compound1-(1-butenyl)-3-nicotinoylpyrrolidine-2-one of the formula:

comprising: condensing nicotinic acid ester withN-(1-butenyl)-2-pyrrolidone in a suitable solvent using a base.
 2. Aprocess as in claim 1 wherein the solvent used is dimethylformamide ortetrahydrofuran.
 3. A process as in claim 1 wherein the base used issodium hydride.